As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased. Among such secondary batteries is a lithium secondary battery having high energy density and operating voltage and excellent preservation and service-life characteristics, which has been widely used as an energy source for various electronic products as well as for the mobile devices.
Based on their external and internal structures, secondary batteries are generally classified into a cylindrical battery, a prismatic battery, and a pouch-shaped battery. Especially, the prismatic battery and the pouch-shaped battery, which can be stacked with high integration and have a small width to length ratio, have attracted considerable attention.
Also, the secondary batteries have attracted considerable attention as an energy source for electric vehicles and hybrid electric vehicles, which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel. As a result, the secondary batteries are being applied to an increasing number of applications owing to advantages thereof, and, in the future, the secondary batteries are expected to be applied to even more applications and products.
As applications and products, to which the secondary batteries are applicable, are increased, kinds of batteries are also increased so that the batteries can provide powers and capacities corresponding to the various applications and products. In addition, there is a strong need to reduce the size and weight of the batteries applied to the corresponding applications and products.
For example, small-sized mobile devices, such as mobile phones, personal digital assistants (PDAs), digital cameras, and laptop computers, use one or several small-sized, lightweight battery cells for each device according to the reduction in size and weight of the corresponding products. On the other hand, middle or large-sized devices, such as electric bicycles and hybrid electric vehicles, use a battery module (which may also be referred to as a “middle or large-sized battery pack”) having a plurality of battery cells electrically connected with each other because high power and large capacity are necessary for the middle or large-sized devices. The size and weight of the battery module is directly related to an accommodation space and power of the corresponding middle or large-sized device. For this reason, manufacturers are trying to manufacture small-sized, lightweight battery modules.
Meanwhile, when battery cells are connected to each other, in a state in which the battery cells are stacked, so as to increase the capacities of battery modules, the dissipation of heat from the battery cells becomes serious. For lithium secondary batteries, heat is generated from the lithium secondary batteries during the charge and discharge of the lithium secondary batteries. If the heat is not effectively removed from the lithium secondary batteries, the heat accumulates in the respective lithium secondary batteries, resulting in the deterioration of the lithium secondary batteries, and the safety of the lithium secondary batteries is greatly lowered. In particular, for a battery requiring high-speed charging and discharging characteristics as in a power source for electric vehicles and hybrid electric vehicles, a large amount of heat is generated from the battery when the battery instantaneously provides high power.
Also, a pouch-shaped battery cell, widely used as a unit cell of each of the battery modules, is configured to have a structure in which an electrode assembly is mounted in a pouch-shaped battery case formed of laminate sheets, and the edge of the battery case is thermally welded by applying pressure to the edge of the battery case while heating the edge of the battery case. However, the safety of such a battery cell structure is relatively low. Specifically, sealing force of the pouch-shaped battery cell is decided based upon coupling force of the edge of the battery case thermally welded. When high pressure is generate in the battery cell due to deterioration of the battery cell caused by long-term use of the battery cell or the abnormal operation of the battery cell, the thermally welded edge of the battery case is widened with the result that gas and an electrolyte may leak from the battery cell. Since the electrolyte contains a combustible material, the battery call may easily catch fire.
In addition, the laminate sheets constituting the battery case has lower mechanical strength than a metal container. Also, each of the laminate sheets has a polymer material exhibiting low thermal conductivity coated on the surface thereof with the result that it is difficult to effectively lower the overall temperature of the battery cell.
In connection with this matter, for example, Japanese Patent Application Publication No. 2004-031281 discloses a cooling structure of an electrode stacked type battery configured to have a structure in which a pair of laminate films each including a metal layer and a resin layer are disposed at opposite sides of an electrode assembly manufactured by stacking a cathode and an anode in a state in which a separator is disposed between the cathode and the anode, and edges of the laminate films are fixed to each other in a tight contact manner, wherein a pair of pushing members push opposite sides of the electrode stacked type battery, the pushing members protrude more outward than the edge of the electrode stacked type battery, the protruding regions of the pushing members function as heat dissipation members which dissipate heat generated from the electrode stacked type battery.
However, the above-mentioned technology has problems in that it is necessary to manufacture a battery cell case in a complicated structure and mount the manufactured battery cell case into a battery, which is troublesome. In addition, the battery cell may be exposed to water or air with the result that the battery cell may be damaged. Also, the above-mentioned technology is limited to a structure in which an air cooling type cooling fin is applied upon stacking of batteries to manufacture a battery module with the result that it is difficult to standardize a fundamental battery module.
The battery case sheets, each of which is configured in a laminate structure including an outer covering layer, a metal blocking layer and an inner sealant layer, are sealed by thermal welding. However, the ends (cut edges) of the laminate sheets are exposed to the outside. As a result, insulation resistance of the battery cell may be lowered due to the exposed metal blocking layers, or external moisture and air may permeate the battery through the sealed portion.
Exposure of the metal blocking layers from the laminate sheets or electrical connection of the exposed metal blocking layers to other regions of the battery may be referred to as destruction (or deterioration) of insulation resistance. The deterioration of insulation resistance lowers the safety and service-life characteristics of the battery, which is not preferable. Also, moisture, introduced into the battery through the sealed portion exposed from the ends of the laminate sheets, reacts to an electrolyte of the battery with the result that gas is generated and the deterioration of the battery is accelerated, lowering the safety and service-life characteristics of the battery, which is not also preferable.
Therefore, there is a high necessity for technology that is capable of fundamentally solving the above-mentioned problems.